xmmstcl lets you control XMMS playback, skip, pause, change the playlist, change skins, and do everything else provided by the xmms_remote_* methods, which is almost everything from the standard user interface. It also has some things not available there, such as "XMMS onchange" which lets your Tcl/Tk application know when something happens in the player. The companion "TkPlayer" has samples for the most important functions and will keep XMMS busy by generating random playlists with songs that you haven't heard in a while.
Xoscope (or oscope) is a digital oscilloscope using input from a sound card or EsounD and/or a ProbeScope/osziFOX. Its features include 8 simultaneous signal displays, 1 us/div to 2 s/div time scale, built-in and external math functions including inverse, sum, diff, avg, xy, and FFT, 23 memory buffers, 5 automatic measurements, and file save/load.
xwax allows DJs and turntablists to playback digital audio files controlled using normal turntables via timecoded vinyl. It handles needle drops, pitch changes, scratching, spinbacks, and rewinds, making it a capable tool for beat-mixing and scratch-mixing. It focuses on an accurate vinyl feel that is efficient, stable, and fast.